That Name is Taken

This error means another character with the same name already exists on your realm. 

• If the character with the same name belongs to you, you can delete the character that has the name.
• If the character with the same name belongs to another player, you must choose another name.

All the character names in a Battle.net account automatically become available after the Battle.net account remained inactive for two expansions. Blizzard Customer Support will not help with releasing the name of a character for you, even if the player who has the name has stopped playing.

Blizzard Customer Support will not release names at all for WoW Classic or Wrath of the Lich King Classic, regardless of how long the account or character has been inactive.